The present invention relates to methods of media authentication, and, more particularly, to a method for authenticating Compact Disc digital optical media.
The term "Compact Disc" herein denotes digital optical media including, but not limited to, media such as Compact Disc Audio (CD) and Compact Disc Read-Only Memory (CD-ROM). The Compact Disc is well-known in the art and has become common for a broad variety of important data storage and information distribution applications. In particular, certain proprietary materials such as computer software, specialized data, and audio/video content are commonly sold and distributed on Compact Disc.
Compact Disc technology is established according to a series of international publications, herein referred to as "standards", all of which are incorporated herein by reference as if set forth fully herein. For example, some common standards applicable to CD's include: the International Standards Organization (ISO) standard 9660 entitled "Information Processing--Volume and File Structure of CD-ROM for Information Interchange, ISO Standard 13490-1", the International Electrotechnique Commission (CEI-IEC) standard 908, generally conforming to what is known as the "Red Book", and ISO/IEC 10140, generally conforming to what is known as the "Yellow Book". A useful summary of the various standards and data formats is found in Compact Disc Terminology, by Busk, Summers, Langer, and Fricks, published by Disc Manufacturing, Inc., Wilmington, Del.
Software and document data may be read and utilized by a computer from CD-ROM, and there are widely-available players for reading data from CD-ROM and using this data to reconstruct audio, visual, text, and audio-visual information. The term "player" herein denotes any device which is able to read data from Compact Disc. Players include, but are not limited to, CD players, CD-ROM multi-media players, DVD players, and game-playing systems, which can reproduce sound, images, and text from data stored on CD. Some computers are also configured with hardware and software capable of accessing CD, to duplicate the functionality of CD players, CD-ROM multi-media players, and game-playing systems.
Unfortunately, it is easy to copy proprietary material from an original Compact Disc Compact Disc and thereby produce an unauthorized copy whose sale and distribution cannot be controlled by the owner of the proprietary material. Individual users can freely copy such proprietary material using low-cost consumer devices such as CD-R recorders (herein referred to as "ordinary consumer Compact Disc recording equipment"), and it is also possible to mass-produce unauthorized copies of proprietary material using equipment such as commercial mastering, pressing, and stamping apparatus (herein referred to as "commercial replicating equipment"). It is usually difficult or impossible to enforce copyright laws in such cases, especially in the case of widespread copying by consumers using ordinary consumer Compact Disc recording equipment, and the legitimate owner of the proprietary material is thereby deprived of the legal right to control the sale and distribution of the proprietary material. The term "original Compact Disc" as used herein refers to an instance of a Compact Disc which has been authorized by and issued under the control of the owner of the proprietary material recorded thereon. In contrast, the term "unauthorized copy" herein denotes an instance of a Compact Disc which has derived from an original Compact Disc via copying that has neither been authorized by nor is under control of the owner of the proprietary material recorded thereon.
Thus, there is a widely-recognized need for a means of distinguishing an original Compact Disc from an unauthorized copy, and especially, there is a widely-recognized need for a means of automatically distinguishing an original Compact Disc from an unauthorized copy. The term "automatically distinguish" herein denotes a means of distinguishing an original Compact Disc from an unauthorized copy in such a way that does not require visual inspection or other human intervention. In particular, automatically distinguishing an original Compact Disc from an unauthorized copy ideally should be feasible by a player as it reads the Compact Disc. That is, whatever distinguishing features are placed on an original Compact Disc for identification as an original Compact Disc, the distinguishing features must be machine-readable. The terms "authenticate", "authentication", and "authenticating" herein refer to any process by which an undetermined instance of a Compact Disc corresponding to an original Compact Disc can be differentiated to be an original Compact Disc as distinct from an unauthorized copy of an original Compact Disc. The term "original Compact Discs to be authenticated" herein denotes all authorized copies which may be derived from a specific original Compact Disc for which the owner of the proprietary material recorded thereon wishes to have means of authentication. The term "undetermined" herein denotes that a specific instance of a Compact Disc is not yet known to be an original Compact Disc as distinct from an unauthorized copy. The term "corresponding to" herein denotes that a specific instance of a Compact Disc contains the same functional data or information as a given original Compact Disc. It will be appreciated that an unauthorized copy of a Compact Disc can appear to be an original Compact Disc even under close physical examination. In addition, it will be appreciated that the data or information content of an unauthorized copy of a Compact Disc can be identical to that of an original Compact Disc. Hence, until a satisfactory authentication process is completed, it will be appreciated that every instance of a Compact Disc from the set of all copies of original Compact Discs to be authenticated can be considered to be undetermined.
In addition to allowing a player to identify the Compact Disc being played as an original Compact Disc rather than an unauthorized copy, a method for authenticating an undetermined Compact Disc can allow the player to selectively access proprietary material only if the Compact Disc is an original Compact Disc, and deny access to the proprietary material if the Compact Disc is an unauthorized copy. Such selective access is a means of copy protection, and can be implemented through various techniques well-known in the art, such as by encrypting the proprietary material and storing a decryption key on the original Compact Disc in such a way that the decryption key is not readily copyable. The presence of a valid decryption key on a Compact Disc therefore is intended to automatically distinguish the Compact Disc as an original Compact Disc, and moreover to provide copy protection by allowing the player access to the proprietary material only if the Compact Disc is an original Compact Disc. The term "copy protection" herein denotes any method or system which either prevents the making of an unauthorized copy or renders an unauthorized copy useless for its intended application.
There are currently a number of schemes which attempt to automatically distinguish an original Compact Disc from an unauthorized copy by storing a special pattern, such as a decryption key, on the Compact Disc in such a way that the special pattern is not readily copyable. For example, U.S. Pat. No. 5,400,319 to Fite et al. ("CD-ROM with Machine-Readable I.D. Code") discloses the use of a laser to selectively destroy portions of the reflective layer of the CD-ROM, thereby creating addressable defects in which a serial number may be encoded. U.S. Pat. No. 5,563,947 to Kikinis ("CD-PROM") discloses a similar use of a laser to physically damage selected sectors and thereby produce a pattern of unreadable sectors in which a decryption key may be stored. And U.S. Pat. No. 5,703,858 to Mitchell et al. ("System for Encoding a Glass Master to Enable Detection of a Counterfeit Optical CD-ROM") discloses the use of a high-frequency random modulation of a laser to produce random defects in the CD-ROM at the master level by selective destruction of predetermined sectors. All of these techniques, as well as other currently-available commercial techniques for copy-protecting a Compact Disc, involve creating damaged or otherwise unreadable portions of the Compact Disc. The theory behind such techniques is that ordinary consumer Compact Disc recording equipment is not intended to produce defects in the recorded copies made therewith, and therefore an unauthorized copy produced on such equipment should lack the unreadable areas in which the decryption key or other pattern is encoded. If this were in fact reliably the case, then such techniques would provide means for authenticating an undetermined Compact Disc. The present inventor, however, has found that it is possible to reproduce unreadable sectors in a copy by using ordinary consumer Compact Disc recording equipment with the appropriate software. Thus, a person with access to such appropriate software would be able to easily defeat such schemes relying on unreadable sectors and thereby create an unauthorized copy of a Compact Disc which will be incorrectly discerned by these authenticating schemes to be an original Compact Disc. In effect, all the schemes currently known in the art for providing copy protection of Compact Disc by encoding patterns in damaged or unreadable data areas are of limited value in distinguishing an original Compact Disc from an unauthorized copy and offer only limited protection against making unauthorized copies.
International Publication No. WO 98/08180 of PCT/IL97/00266 by the present inventor et al., which is incorporated by reference for all purposes as if fully set forth herein, discloses a method for authenticating digital optical media by recording and reading two classes of invalid symbols on the digital optical media. One class of invalid symbol is referred to as an "ambiguous symbol". An ambiguous symbol is a non-standard symbol, and is characterized by having two distinct data values instead of a single data value (an ambiguous symbol may therefore also be referred to as a "bistable symbol", and these two terms are herein interchangeable). Having a single data value is a characteristic of a standard symbol. When reading an ambiguous symbol, however, the physics of the reading process is such that one of the two distinct data values is read randomly. An ambiguous symbol may be detected by reading a given symbol a number of times and comparing the results. If the same data value always is returned, the given symbol is a standard symbol. In contrast, if different data values are returned, then the given symbol is an ambiguous symbol. Hence, an ambiguous symbol encodes invalid data herein termed "ambiguous data". Writing ambiguous symbols requires special hardware, and therefore ambiguous symbols are not reproducible by ordinary digital optical media recording equipment. Consequently, the presence or absence of these ambiguous symbols serves to confirm or deny, respectively, the authenticity of a specific instance of digital optical media: provided that the original digital optical media were produced with these ambiguous symbols, then a specific instance of the digital optical media having the ambiguous symbols may be determined to be authentic, whereas a specific instance of the digital optical media lacking the ambiguous symbols may be determined to be an unauthorized copy. In order to make a determination of the authenticity of a specific instance of digital optical media, the it must be possible to detect the presence of the ambiguous symbols using an ordinary player of the digital optical media. Ambiguous symbols, however, are considered according to the standards to be errors, and the player's error-correcting mechanism attempts to correct the ambiguous symbols to have a single value. If the player is successful in correcting ambiguous symbols, then ambiguous symbols will not be detectable using that player. Therefore, International Publication No. WO 98/08180 of PCT/IL97/00266 also discloses a method of overriding the error-correction of a player by recording a second class of invalid symbols on the original digital optical media in such a way as to disable the error-correcting mechanism for the ambiguous symbols. (A symbol belonging to this second class of invalid symbols is herein referred to as an "undefined symbol", and is characterized by not having a data value assignment in the standards. There are a total of nine such undefined symbols for Compact Disc, and they are immediately detected as invalid symbols by a Compact Disc player, as opposed to invalid symbols which are defined in the standards, but which have incorrect data values and which require processing by the player's error-detection mechanism and/or error-correcting mechanism in order for the player to detect them as invalid symbols.) Unfortunately, however, the published standards for digital optical media contain specifications for only the digital optical media and do not contain any specifications for players of the digital optical media. Consequently, there are no universal standards for players of digital optical media. As a result, the capabilities of the players vary considerably from one player to another, and therefore the method disclosed in International Publication No. WO 98/08180 of PCT/IL97/00266 may not work with all players of digital optical media. With certain players, it may not be possible to detect ambiguous symbols because of the specific error-correcting mechanisms of those players.
Therefore, it would be highly advantageous to have a method and system for authenticating an undetermined digital optical media which cannot be defeated utilizing commercially-available copying equipment, regardless of the software employed, and which will be usable with all players of the digital optical media. This goal is met by the present invention for use with Compact Disc digital optical media.